From 44bcd58051919e62fdbaa8ba823b7bdff575b6c6 Mon Sep 17 00:00:00 2001
From: Max Rossmannek <max.rossmannek@uzh.ch>
Date: Sat, 21 Nov 2020 14:38:15 +0100
Subject: [PATCH] Fix Undo command

The Undo command broke in 48dff11 when the `onModify` hook got added to
its execution in order to fix #2213. The reason for it begin broke is
that a Task object is created in an unsafe manner because the `prior`
task may be empty.
Catching this case fixes the bug.
---
 src/TDB2.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/TDB2.cpp b/src/TDB2.cpp
index ee6c38de7..353f3ac4b 100644
--- a/src/TDB2.cpp
+++ b/src/TDB2.cpp
@@ -839,7 +839,9 @@ void TDB2::revert ()
     //   - erase from completed
     //   - if in backlog, erase, else cannot undo
 
-    Task old = Task (prior);
+    Task old = Task ();
+    if (prior != "")
+      old = Task (prior);
     Context::getContext ().hooks.onModify (Task (current), old);
 
     // Modify other data files accordingly.